Polymer solutions with shear reversible properties

ABSTRACT

Water-based fluids that can viscosify under shear or can produce a gel or form a gel under shear are obtained by dissolving polymers in an aqueous phase. These polymers comprise three types of functional groups: non-ionic functional groups that are hydrosoluble at the temperature under consideration, ionic functional groups, and functional groups that are hydrophobic at the temperature under consideration. These three types of functional groups can be distributed or spread in a random distribution along the polymer chain. A slightly block distribution is acceptable. For applications to oil wells, functional groups are used which exhibit LCST (Lower Critical Solution Temperature) behavior (i.e., a low critical solution temperature) instead of hydrophobic functional groups. At temperatures below the LCST, the functional groups are hydrophobic.

The present invention relates to polymers that can be used to preparefluids that gel under shear or that viscosify under shear when they aredissolved in an aqueous medium. The term “fluids that viscosify undershear” as used here and throughout the present application means fluidswith a viscosity that increases when shear is applied. Such an increasein viscosity is reversible, when the shear is reduced. The term “fluidsthat gel under shear” as used here and throughout the presentapplication means fluids that can form a gel when shear is applied. Thegel is reversible and disappears or is destroyed when the shear isreduced or stopped. Such behavior is in contrast to the behavior ofnormal polymer solutions wherein, when the solution is sheared, theviscosity reduces, or the gel is destroyed in the case when a gel isformed.

Such products have a number of applications to drilling, to eliminatingwell or reservoir damage, to fracturing and completion ofhydrocarbon-producing wells, geothermal wells and analogous wellbores,and to the field of stimulation techniques intended to optimize therecovery of fluids contained in geological reservoirs. Such products canalso be used in numerous other industries, such as vibrationattenuators, clutches, in the design of liquids that are transformedinto creams when applied and rubbed onto the skin or any other surface,and fluids used to initiate the transmission of shear movement or waves(shear waves are transmitted through a substance in the form of a gelbut not through a liquid). Such non-limiting examples demonstrate thatthe field of application of such substances is extremely wide and coversmany different industrial fields.

In the industry corresponding to the field of drillinghydrocarbon-producing wells, a large number of water-soluble (orhydrosoluble) polymers are used that have gelation or viscosifyingproperties. The most frequently used polymers, such as naturalpolysaccharides, endow a solution with non-Newtonian properties with lowviscosity at high shear rates and high viscosity at rest (shear-thinningfluids). For many applications, however, the opposite behavior isdesired (rheo-viscosifying behavior). A known method of secondaryhydrocarbon recovery consists in injecting a flushing fluid—such aswater to which polymers have been added in order to increase itsviscosity—in order to flush the hydrocarbons towards the productionwell. A fluid in which the viscosity increases reversibly with shearrate could minimize problems with viscous fingering, and could renderthe displacement front uniform, preventing the formation of pockets ofhydrocarbons that have not been flushed. In non-homogeneous reservoirformations where permeability varies from one zone to the next, and incontrast to shear-thinning fluids, rheo-viscosifying fluids minimize thedifference in fluid flow rate, reducing by-pass of low permeabilityzones. When reservoirs exhibit fractures, fluids that viscosify undershear reduce the extent to which porous zones are bypassed by theflooding fluid passing through or via the fracture path (for example insandstone reservoirs), or to which the narrowest fractures are bypassedto the advantage of the largest fractures (for example, in carbonatereservoirs). Injecting a fluid that gels under shear, in conjunctionwith suitable pumping conditions, would reduce the width of the largestfractures where shear is higher but would not reduce the width of thenarrowest fractures where shear is lower. Thus, in fractured reservoirs,the best way to reduce oil by-pass consists firstly, in pumping a fluidthat gels under shear, and then in pumping a fluid that viscositiesunder shear.

International patent application WO 99/38931 describes fluidcompositions comprising precipitated silica nanoparticles and ahydrosoluble copolymer comprising one or more monomers with little or noaffinity for silica, and one or more co-monomers that are adsorbed ontothe silica. Such compositions are highly effective when preparing fluidsthat either viscosify under shear or gel under shear. Because of theirnanometer scale, the nanoparticle fraction in the components in questionmust be taken up into suspension in a liquid. For small operations, suchas temporary protection of a reservoir formation, such a step is not aproblem, but for operations such as enhanced oil recovery (EOR), inwhich large or very large quantities have to be pumped, this can causelogistical problems on-site.

Despite the innovation of WO99/38931, there still exists a great needfor fluids that viscosify under shear or that gel under shear, obtainedor prepared by using water to dissolve solid components that can betransported in sacks, thereby making logistics cheaper, and requiringsmaller storage and intermediate storage volumes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 respectively show the different types of viscositybehavior.

The present invention proposes water-based fluids that can viscosifyunder shear or can produce a gel or form a gel under shear, and that areobtained by dissolving polymers as defined below in an aqueous phase.These polymers comprise three types of functional groups: non-ionicfunctional groups that are hydrosoluble at the temperature underconsideration, ionic functional groups, and functional groups that arehydrophobic at the temperature under consideration. The term “functionalgroups that are hydrosoluble at the temperature under consideration”means functional groups that might be hydrophobic at a differenttemperature, but which are hydrosoluble at the temperature at whichshear-thickening or gel formation under shear is to occur. The term“functional groups that are hydrophobic at the temperature underconsideration” means that the site might be hydrophilic at a differenttemperature, but the site is insoluble in water at the temperature atwhich shear-thickening or gelation or setting into a gel is to occur.These three types of functional group are preferably spread ordistributed randomly along the polymer chain. Partial or complete blockdistribution of functional groups in the polymer chain is lesspreferred.

A particularly preferred feature of the present invention forapplications to oil wells resides in the use of functional groupsexhibiting LCST (Lower Critical Solution Temperature) behavior (i.e., alow critical solution temperature) instead of hydrophobic functionalgroups. At temperatures below the LCST, the functional groups arehydrophilic. In that case, the polymer chains do not associate togetherand the solution behaves like a conventional Newtonian fluid or like ashear-thinning fluid. This allows easy pumping into the well and intothe porous formation or into fractures or cracks close to the wellbore.Slightly above the LCST temperature, the functional groups becomehydrophobic and the behaviour of thickening or of forming a gel undershear appears in accordance with the present invention. Because of thegeothermal temperature gradient, the fluid is progressively heated as itdescends into the hole. The fluid is thus very easy to place, andviscosification or gel formation does not appear when it is not desired.For this reason, it is highly preferable in the present invention to usehydrophobic functional groups exhibiting LCST behavior. A non-exhaustivelist of LCST type chemicals is provided in the article by Taylor et al.,J. Polymer Science, 13, 2551-2570 (1975). This list is non-exhaustiveand does not limit the present invention, and is provided solely by wayof example Further, the LCST of the fluid can be adjusted to the desiredtemperature by adding free LCST type chemicals, i.e., chemicals that arenot bonded to the polymer, this addition being made to the polymersolution.

To attempt an explanation and propose a better comprehension of theinvention, which must not, however, be considered as limiting thepresent invention, the following possible action mechanism has beenproposed. At the temperature under consideration, hydrophobic units formassociation nodes that can be ruptured or destroyed by applying shear.The associations, which are intra-molecular associations, reorganizethemselves and become intermolecular under shear. This increases theapparent molecular weight of the macromolecules, and thus increases theviscosity of the solution. If the network constructed or formed by thenodes becomes three-dimensional, a gel will appear. Incorporatingrepulsive ionic units tends to stretch the polymer domains or poolsslightly, limiting intra-molecular node multiplication and favoring achange in configuration to inter-molecular nodes with more stretchedpolymer chains. At the temperature under consideration, non-ionichydrosoluble units provide macromolecules with a certain flexibility andmobility, increasing their solution entropy, and encouraging theformation of intra-molecular nodes on standing.

Different methods exist for incorporating the functional groups into thefinal polymer.

-   A) These functional groups can be incorporated by copolymerization    or co-condensation of different monomers. In this case, at least two    different monomers must be used: a monomer that provides the    non-ionic hydrosoluble functional groups and a further monomer that    provides the ionic functional groups and the hydrophobic functional    groups. It is possible to use more than two co-monomers. The    following combinations are given by way of non-limiting example:    -   Three different co-monomers, each providing one of the        above-mentioned desired functional groups, a non-ionic        hydrosoluble monomer, an ionic monomer, and an LCST or        hydrophobic monomer.    -   It is also possible to provide the same type of site using more        than one monomer, for example a terpolymer comprising two        different co-monomers providing the non-ionic hydrosoluble        functional groups, and an ionic co-monomer comprising ionic        functional groups and hydrophobic functional groups, or a        copolymer comprising four co-monomers, one providing the        non-ionic hydrosoluble functional groups, another providing        hydrophobic functional groups, and two co-monomers providing        ionic functional groups with the same type of charge, i.e.,        anionic or cationic. It is also possible to consider the use of        a copolymer incorporating four co-monomers, one providing        non-ionic hydrosoluble functional groups, a further providing        ionic functional groups, and two co-monomers providing        hydrophobic functional groups. The number of co-monomers is not        limited, provided that the three types of functional groups are        properly incorporated into the copolymer, with no ionic        functional groups carrying opposite charges.-   B) The non-ionic hydrosoluble functional groups, the ionic    functional groups and the hydrophobic functional groups can be added    to an existing polymer by means of chemical reactions using    reactants capable of reacting with the polymer. The reactions can    incorporate grafting or hydrolysis reactions. Some non limiting    examples are given below to illustrate this implementation:    -   It is possible to graft fatty amines to carboxylic acid        functional groups to form an amide site substituted by an allyl        chain or to use fatty alcohols to produce or form ester        functional groups. The acidic functional groups will then become        hydrophobic.    -   It is possible to hydrolyze several ester or amide functional        groups to form acidic functional groups.    -   It is possible to combine the above two reactions to form the        final polymer of the invention. Starting from a polyacrylamide,        this can be partially hydrolyzed to create acidic functional        groups on the polymer chain. A portion of the carboxylic        functional groups created can then be reacted with a fatty        amine, using a coupling agent to form the final polymer;    -   It is also possible to react the acidic functional groups with        an amine comprising one or more short alkyl radical type        substituent(s), to form non-ionic hydrosoluble functional        groups. As an example, starting from a polyacrylic acid, and        causing methylamine or dimethylamine to react with a fatty        amine, a polymer of the invention will be formed.    -   Amine quaternization represents a reaction for introducing a        cationic site to a polymer containing mobile hydrogen atoms.    -   The above examples are not limiting but serve to demonstrate        simply that a number of routes that are already known to the        skilled person exist for synthesizing the polymer of the        invention, using known means, methods and materials for forming        polymers.-   C) Any combination of A) and B) can be used.

The final polymer of the present invention has a molecular weight ofmore than 300,000 g/mole, preferably more than 500,000 g/mole.

If the final polymer has been synthesized using route A), it willcontain the following quantities of the three types of functional groupsof the invention:

-   -   The proportion of hydrophobic units at the temperature under        consideration or LCST units will be more than 0.1 mole % of        monomer units, preferably more than 0.5 mole % of monomer units.        This proportion must also be less than 30 mole % of monomer        units, preferably less than 25 mole % of monomer units. This        proportion is also limited by the solubility of the final        polymer in water at the temperature under consideration. As an        example, at ambient temperature, using N,N-dimethylacrylamide as        the non-ionic hydrosoluble monomer, the proportion of —C₁₂H₂₅        will be limited to less than 20%, and the proportion of —C₁₈H₃₇        groups will be limited to less than 10%. Fluorinated hydrophobic        functional groups can be used as well as hydrogenated functional        groups. The proportion of —(CH₂)_(m)—(CF₂)_(n)—X (X=H or F)        groups will be less than 10%, with the condition m+n<19 and m<19        if n=0 and n<12 if m=0. Any combination of these two types is        possible in the present invention.    -   The proportion of ionic units will be more than 0.1 mole % of        monomer units, preferably more than 0.5 mole % of monomer units.        This proportion will also be less than 30 mole % of monomer        units.    -   The proportion of non-ionic hydrosoluble monomer units at the        temperature under consideration will be more than 40 mole % of        monomer units.

If the polymer has been produced or synthesized using either route B) orroute C), the monomer units will be considered as if the polymer hadbeen produced using route A), but using monomers already modified usingthe reactions involved in routes B) or C). The concentration limitsmentioned above will then be the same as those also given above.

The mixing water can contain dissolved added salts, provided that thepolymer remains soluble at the temperature under consideration. As anexample, with the most soluble non-ionic hydrosoluble monomers such asacrylamide, the amount of salt can be less than 1 mole/liter at ambienttemperature. With the least soluble non-ionic hydrosoluble monomers suchas N,N′-dimethylacrylamide, the amount of salt can be less than 0.1mole/liter.

If the polymer contains LCST functional groups, free LCST type chemicalsubstances can be added, i.e., chemical substances that are notchemically bonded to the polymer, addition being made to the mixingwater to modify the association temperature of the fluid.

It is also possible to add surfactants to the polymer solution. Theeffect will be to modify the critical shear rate above which thesolution will start to viscosify or form a gel. Such surfactants can benon-ionic, ionic with the same charge or charges as the polymer, orionic with one or more opposite charges.

-   -   Non-ionic surfactants: The concentration of surfactant must be        less than 50 times the concentration of hydrophobic functional        groups in the polymer, preferably less than 10 times. Adding a        surfactant induces a variation in the critical shear rate, and        this variation represents either an increase or a decrease        depending on the concentration of surfactant. However, the        shear-thickening effect disappears when the concentration of        surfactant is more than 10 times the concentration of        hydrophobic functional groups in the polymer.    -   Examples of surfactants: C_(n)E_(m) (7<n<22 and 3<m<24).    -   Ionic surfactants with the same charge or charges as the        polymer: The concentration of surfactant must be more than 50        times the concentration of hydrophobic polymer functional groups        and preferably less than 10 times. The effect of the ionic        surfactant is substantially the same as that of the neutral        surfactant.    -   Examples of surfactants: Sodium alkylsulfate;    -   Ionic surfactant with opposite charge or charges: The        concentration of surfactant must be less than 50 times the        concentration of hydrophobic functional groups in the polymer        and preferably less than 10 times.    -   The effect of the ionic surfactant is substantially the same as        that of the neutral surfactant;    -   Examples of surfactant: Alkyltrimethylammonium bromide.

While the present invention can function with any of the polymersdefined above, the following monomers are highly preferred:

-   -   Non-ionic hydrosoluble monomers: Highly preferred monomers for        use in the context of the invention are acrylamide, its N        substituted hydrosoluble derivatives, and hydrosoluble        N-vinylamides such as N-vinylacetamide. This list includes        N-isopropylacrylamide (NiPAM), except when the co-monomer is        MADAP (N,N-[(dimethylamino)propyl]methacrylamide), with its        amine site quaternized by an alkyl chain:

-   -    where R₁=H to C_(n)H_(2n+1) and R₂=H or CH₃.    -   Ionic monomers: Highly preferred anionic monomers for use in the        context of the invention are acrylic acid, methacrylic acid,        maleic anhydride, AMS (acrylamidomethylpropylsulfonate),        styrenesulfonic acid or vinylsulfonic acid.        -   Highly preferred cationic monomers are quaternised or            non-quaternised vinylpyridine with a pH of less than 2,            quaternised or non-quaternised N-vinylimidazole with a pH of            less than 7 and monomers with the following two general            formulae:

-   -    where R₁=H or CH₃, A=O or NH, R₂=(CH₂)_(n) where n=1 to 3, R₃        and R₅=H or CH₃, R₄=H to C_(m)H_(2m+1). The maximum value of m        is a function of the temperature under consideration. These two        monomers simultaneously provide the ionic and the hydrophobic        function. They can be incorporated into the polymer using any of        routes A), B) or C). The higher the temperature, the higher the        value of m. At ambient temperature, m is preferably less than        22, more preferably less than 20. Substituent R₄ can also be a        perfluorinated alkyl chain or any entity between a        perfluorinated alkyl chain and an alkyl chain. A mixture of        monomers with different substituents can also be highly        effective in order to produce a more gradual increase in gel        formation or viscosity.    -   Hydrophobic monomers: Particularly preferred hydrophobic        monomers for use in the context of the invention are those from        the following family of monomers:

-   -    where R₁=H or CH₃, A=O or NH, R₄=C_(n)H_(2n+1). The minimum        value of n is 8. The value of n is a function of the temperature        under consideration. These monomers can be incorporated into the        polymer using any one of routes A), B) or C). The higher the        temperature, the larger the range of n. At ambient temperature,        n preferably satisfies the condition 8<n<22, more preferably        10<n<20. Substituent R₄ can also be a perfluorinated alkyl chain        or any entity between a perfluorinated alkyl chain and an alkyl        chain. It is also possible to use hydrophobic silanes and        silicones. A mixture of monomers containing different        substituents can also be highly effective to produce a more        gradual increase in gel formation or viscosity.

By varying the pH of the polymer solution, its Theological behavior canbe varied. Four basic situations exist, depending on the type of ionsincorporated into the polymer, as well as intermediate situations orcases when different types of ions with the same charge sign areincorporated into the polymer, or when there are different types ofcharges on a single chain, or again a mixture of polymers with differenttypes of charges of the same sign.

-   -   Weak acid functional groups (negatively charged polymer). When        the pH falls below the pK of the weak acid functional groups,        pH<pK, the polymer solution behaves as a Newtonian fluid up to        shear rates of more than 1000 s⁻¹. Weak acid functional groups        can be provided by carboxylic acid functional groups, for        example.    -   Strong acid functional groups (negatively charged polymer). The        polymer solution will retain its gelation/viscosification        behavior under shear at all values of pH. Strong acid functional        groups can, for example, be provided by sulfonic functional        groups.    -   Weak base functional groups (positively charged polymer). When        the pH is increased above the pK of the weak base functional        groups, pH<pK, the polymer solution behaves as a Newtonian fluid        up to shear rates of more than 1000 s⁻¹. Weak base functional        groups can be provided by non-quaternised amine functional        groups, for example.    -   Strong base functional groups (positively charged polymer). The        polymer solution will retain its gelation/viscosification        behavior under shear at all values of pH. Strong base functional        groups can, for example, be provided by quaternised amine        functional groups (if the amizes are quaternised by protons,        they are weak bases; if they are quaternised by alkyl groups,        they are no longer bases).

When using mixed charged polymers (with the same charge sign), theirsolution will have the properties of the two types in a proportion andin an amount depending on the proportions of the charge types.

If desired, buffers can be added to the polymer solutions to modify thepH to a limited extent, when the fluid is pumped into zones with a highor low pH.

The above properties can be very useful for producing delayed pHmodification properties (using means that are known to the skilledperson), such as Newtonian behavior during pumping and placement of thepolymer solution, and rheo-viscosification/gelation behavior once thefluid has been placed in the desired location.

This facilitated pumping can also be carried out using polymers inaccordance with the present invention in which the hydrophobicfunctional groups of the polymer have been replaced by functional groupsexhibiting LCST. The polymer chains will start to associate just abovethe LCST. The LCST temperature will then be selected so that it is belowthe temperature of the formation to be flushed or completely orpartially plugged. The temperature at which the polymer chain starts toassociate can be modified by adding to the solution free chemicalsubstances exhibiting a LCST, i.e., chemical substances that are notchemically bonded to the polymer.

EXAMPLES

Polymer Synthesis Examples

Route A)

Direct Terpolymerization Example

70 ml of chloroform, 1.5 g of N-dodecylmethacrylamide, 0.5 ml of acrylicacid in its acid form and 5 ml of N,N-dimethylacrylamide were dissolvedin a three-necked flask. The reaction medium was deaerated for one hourby bubbling through nitrogen with stirring. Nitrogen bubbling wasmaintained throughout the reaction. The temperature was then raised to60° C. and 15 mg of an initiator (AIBN) was then added. The reaction wasallowed to progress for 12 hours, then the reaction medium wasprecipitated in 3 l of diethyloxide and vacuum dried overnight atambient temperature.

Route B)

Precursor Synthesis Example

The copolymer precursor syntheses were carried out in water at 30° C.For a copolymer of N,N-dimethylacrylamide (DMA) and acrylic acid (AA),the ratios were 80/20, the monomer concentration was 1 mole/I, the pHwas adjusted to 8 using sodium hydroxide and the solution was deaeratedfor one hour by bubbling through nitrogen prior to introducing ammoniumpersulfate and sodium metabisulfite already separately dissolved in 2cm³ of water. For a molecular mass of more than 2000 kcg/mole, theconcentration of initiators was as follows: [(NH₄)₂S₂O₈]/[monomers]=1%and [(Na₂S₂O₅]/[monomers]=0.03%. was allowed to progress for 4 hours.The final solution was neutralized with HCl to a pH of 4-5, it wasdialyzed and recovered by freeze drying.

Modification Reaction

A 3% solution of precursor in N-methylpyrrolidone (No) was heated withstirring at 60° C. The necessary quantity of alkylamine (the referenceto the alkylamine denotes the number of carbon units constituting thealkyl chain, for example C12 for n-dodecylarine) and this quantity wasadded with a threefold excess of coupling agent(dicyclohexylcarbodiimide). The reaction was allowed for progress for 12hours. The reaction medium was precipitated twice in diethyloxide, andvacuum dried overnight at ambient temperature.

Example of Properties of Polymer Solutions

The polymer solution properties were determined by scanning at a staticshear rate of 10 s⁻¹ per minute in a Couette cell with a sample gap of0.5 mm. The values for the initial viscosity (when the sample behaves asa Newtonian fluid), the critical shear rate (at which the viscositystarts to rise) and the ratios of the maximum viscosity to the initialviscosity were recorded. Unless otherwise indicated, the acrylic groupswere in the basic form, i.e., in the sodium acrylate form.

The polymers in the following examples are denoted by theircompositions:

-   -   DMA=N,N-dimethylacrylamide, AA=acrylic acid or its salts,        Am=acrylamide and xCy is the monomer carrying the alkyl        hydrophobic substituent, y representing the number of carbon        atoms in the alkyl chain;    -   The number preceding the name of the monomer represents the        proportion of said monomer as a mole percentage in the final        copolymer.

Thus, 80DMA/11AA/9C12 means that in the final polymer, there will be 80mole % of N,N-dimethylacrylamide (DMA), 11 mole % of acrylic acid (AA)and 9 mole % of N-alkylacrylamide carrying a N-alkyl chain containing 12carbon atoms.

Example 1

Static scanning was carried out under a shear gradient using a80DMA/11AA/9C12 type polymer (molecular weight MW=3,000,000 g/mole). Thedifferent types of behavior are shown in FIG. 1. The increase inviscosity could be sudden (samples gelation under shear) or continuous(samples viscosifying under shear).

Example 2

A scan test under static shear was carried out using a 80DMA/10AA/10C12type polymer (MW=300,000 g/mole) at a concentration of 40 g/l; scanningwas carried out up to 150 s⁻¹ then back to 0 s⁻¹. The graph obtained isshown in FIG. 2. It can be seen that the viscosification under sheareffect was reversible.

Example 3

A constant static shear rate was applied to a sample of 80DMA/10AA/10C12polymer (MW=2,300,000 g/mole) at a concentration of 10 g/l. The timerequired for gel formation or gelation of the sample was measured and isshown in the table below.

Shear rate 50 100 200 300 350 400 450 600 (s⁻¹) Gel formation 5900 30001900 1400 730 170 9 2 time (s)

Example 4

Scan tests were carried out under static shear on a 80DMA/10AA/10C12type terpolymer and at three different molecular weights and differentpolymer concentrations.

The results are shown in the following table:

Critical shear MW Concentration Initial viscosity rate (g/mole) (g/l)(Pa · s) (s⁻¹) η_(max)/η₀ 306,000 30 0.0073 460 130 40 0.23 82 25 50 1.628 11 900,000 20 0.0071 270 95 25 0.14 44 23 30 0.76 12 11 3,000,000 50.0025 660 83 10 0.0080 140 150 20 0.44 6 29

Example 5

Static shear scan tests were carried out using a modified 80% DMA/20% AAcopolymer precursor (MW=3,000,000 g/mole) with a polymer concentrationof 10 g/l with different amounts of modification and with differenthydrophobic amines.

The results are shown in the table below:

Hydrophobic Initial viscosity Critical shear rate functional groups (Pa· s) (s⁻¹) η_(max)/η₀ 1C12 0.087 49 60 2C12 0.05 70 270 5C12 0.014 113110 10C12 0.008 140 150 15C12 0.004 220 37 5C12 0.014 113 110 5C14 0.007235 34 5C16 0.006 334 40 5C18 0.004 400 61

Example 6

Static shear rate scan tests were carried out with terpolymers modifiedin the hydrophobic compounds by 10 mole % using dodecylamine containingdifferent amounts of charged monomers.

Sodium Initial Critical acrylate Concentration viscosity shear rateComposition (mole %) (%) (Pa · s) (s⁻¹) η_(max)/η₀ 90DMA/1.5AA/8.5C121.5 0.3 0.0050 710 2.5 (MW = 3,000,000 g/mole) 0.5 0.013 230 6.4 1 0.1735 4.2 80DMA/10AA/10C12 10 0.5 0.0025 660 83 (MW = 3,000,000 g/mole) 10.0080 140 150 2 0.44 6 29 70DMA/20AA/10C12 20 2 0.090 1900 20 (MW =2,500,000 g/mole) 2.5 0.22 820 32 3 3.6 40 88

Example 7

When the neutral monomer was a non-substituted actylamide (Am), theviscosification under shear effect appeared with the addition of a salt(in the case sodium chloride). Static shear rate scan tests were carriedout with a 80Am/14AA/6C12 (MW=370,000 g/mole) polymer composition at apolymer concentration of 10 g/l.

The results are shown in the table below:

Initial Critical viscosity shear rate C_(NaCl) (mole/l) (Pa · s) (s⁻¹)η_(max)/η₀ 0.001 3.9 0.3 1.6 0.01 2.4 0.7 2.5 0.1 0.18 3 6.3 1 0.045 112.4

Example 8

A 80DMA/20AA polymer was grafted with P(EOPO) oligomers (MW=2,000g/mole) in an amount of 50% by weight of the final polymer. Theproportion of propylene oxide (PO) to ethylene oxide (EO) was 39/6. Astatic shear rate scan test was carried out at different temperatureswith a polymer concentration of 3 g/l. The sample was of theshear-thinning type at low temperature and shear-thickening at hightemperature (above 30° C.).

The results are shown in the table below:

Initial Critical viscosity shear rate Temperature (Pa · s) (s⁻¹)η_(max)/η₀ 25 0.094 / / 25 0.084 8 3.7 40 0.038 21 29 50 0.023 100 13

Example 9

Static shear rate scan tests were carried out on a 80DMA/18AA/2C12(MW=3,000,000 g/mole) polymer at a concentration of 5 g/l, the preciseproportion of NaCl or HCl being added to the solutions to demonstratethe effect of pH on gelation under shear.

Initial viscosity Critical shear rate pH (Pa · s) (s⁻¹) η_(max)/η₀ 5.10.0027 1830 19 7.3 0.0044 850 41 9.3 0.0064 170 135

Example 10

Static shear rate scan tests were carried out with a 80DMA/15AA/5C12(MW=3,000,000 g/mole) polymer at different concentrations of neutralsurfactant (in this case, C12E8 surfactant).

The results are shown in the following table:

Surfactant concentration Initial viscosity Critical shear rate (mole/l)(Pa · s) (s⁻¹) η_(max)/η₀ 0 0.014 113 110 10⁻⁵ 0.0053 151 220 10⁻³0.0083 99 203 10⁻² 0.024 22 134 10⁻¹ 0.057 420 3.4

Other characteristics and advantages of the invention will be betterunderstood from the following description made with reference to theaccompanying drawings in which:

EXAMPLES

The invention also encompasses all embodiments and applications that aredirectly accessible to the skilled person on perusing the presentapplication from his own experience.

1. A polymer fluid, the polymer comprising: non-ionic hydrosolublefunctional groups corresponding to one or more of the followingmonomers: acrylamide, N substituted acrylamide derivatives andN-vinylamides; ionic functional groups corresponding to one or more ofthe following monomers: acrylic acid, methacrylic acid, maleicanhydride, acrylamidomethylpropylsulphonate, styrene sulphonic acid,vinyl sulphonic acid, vinylpyridine, quaternary ammonium salts ofvinylpyridine, N-vinylimidazole, quaternary ammonium salts ofN-vinylimidazole, and monomers of general formulae:

 where R₁=H or CH₃, A=O or NH, R₂=(CH₂)_(n) where n=1 to 3, R₃ and R₅=Hor CH₃, and R₄=H to C_(m)H_(2m+1), where m is less than 22, orperfluorinated derivatives thereof; and hydrophobic functional groupscorresponding to one or more of the following monomers: monomers ofgeneral formula —(CH₂)_(m)—(CF₂)_(n)—X wherein X=H or F, m+n<19, m<19 ifn=0, and n<12 if m=0, and monomers of general formula:

where R₁=H or CH₃, A=O or NH, R₄=C_(n)H_(2n+1) or perfluorinatedderivatives thereof, and n≧8, a hydrophobic silane, or a silicone; theviscosity of the fluid increasing when the fluid is subjected to shear,wherein the ionic monomers comprise at least one of vinylpyridine with apH of less than 2 or quaternary ammonium salts thereof, andN-vinylimidazole having a pH of less than 7 or quaternary ammonium saltsthereof and wherein the proportion of ionic monomer units in the polymeris more than 0.1 mol %.
 2. The polymer fluid of claim 1, wherein thenon-ionic hydrosoluble monomers comprise at least one ofN,N-dimethylacrylamide, N-vinylacetamide and N-isopropylacrylamide. 3.The polymer fluid of claim 1, wherein the hydrophobic monomer comprisesmonomers of general formula:

where R₁=H or CH₃, A=O or NH, R₄=C_(n)H_(2n+1) or perfluorinatedderivatives thereof, and 8<n<22.
 4. The polymer fluid of claim 3,wherein 10<n<20.
 5. The polymer fluid of claim 1, wherein the polymerhas a molecular weight of more than 300,000.
 6. The polymer fluid ofclaim 5, wherein the polymer has a molecular weight of more than500,000.
 7. The polymer fluid of claim 1, wherein the proportion ofhydrophobic monomer units in the polymer is more than 0.1 mol %.
 8. Thepolymer fluid of claim 7, wherein the proportion of hydrophobic monomerunits in the polymer is more than 0.5 mol %.
 9. The polymer fluid ofclaim 1, wherein the proportion of hydrophobic monomer units in thepolymer is less than 30 mol %.
 10. The polymer fluid of claim 9, whereinthe proportion of hydrophobic monomer units in the polymer is less than25 mol %.
 11. The polymer fluid of claim 1, wherein the proportion ofionic monomer units in the polymer is more than 0.5 mol %.
 12. Thepolymer fluid of claim 1, wherein the proportion of ionic monomer unitsin the polymer is less than 30 mol %.
 13. The polymer fluid of claim 1,wherein the proportion of non-ionic hydrosoluble monomer units in thepolymer is more than 40 mol %.
 14. The polymer fluid of claim 1, whereinthe polymer is mixed with water to form the fluid.
 15. The polymer fluidof claim 14, further comprising at least one non-ionic surfactant. 16.The polymer fluid of claim 15, wherein the concentration of non-ionicsurfactant is less than 50 time the concentration of the hydrophobicfunctional groups in the polymer.
 17. The polymer fluid of claim 16,wherein the concentration of non-ionic surfactant is less than 10 timethe concentration of the hydrophobic functional groups in the polymer.18. The polymer fluid of claim 14, further comprising at least one ionicsurfactant having the same charge as that of the polymer.
 19. Thepolymer fluid of claim 18, wherein the concentration of non-ionicsurfactant is less than 50 time the concentration of the hydrophobicfunctional groups in the polymer.
 20. The polymer fluid of claim 19,wherein the concentration of non-ionic surfactant is less than 10 timethe concentration of the hydrophobic functional groups in the polymer.21. The polymer fluid of claim 14, further comprising at least one ionicsurfactant having an opposite charge to that of the polymer.
 22. Thepolymer fluid of claim 21, wherein the concentration of non-ionicsurfactant is less than 50 time the concentration of the hydrophobicfunctional groups in the polymer.
 23. The polymer fluid of claim 22,wherein the concentration of non-ionic surfactant is less than 10 timethe concentration of the hydrophobic functional groups in the polymer.24. The polymer fluid of claim 14, wherein the polymer is present in aconcentration of 5-50 g/l.
 25. The polymer fluid of claim 14, furthercomprising at least one buffer for modifying the pH of the solution whenin the presence of external pH modifiers.
 26. A method of preparing thepolymer fluid of claim 1, comprising copolymerization or co-condensationof at least two different monomers, one of which provides the non-ionichydrosoluble functional groups and a further monomer that provides theionic functional groups and the hydrophobic functional groups.
 27. Themethod of claim 26, comprising copolymerisation or co-condensation ofthree different co-monomers, each providing one of the functionalgroups.
 28. The method of claim 26, comprising copolymerisation orco-condensation of a terpolymer comprising two different co-monomersproviding the non-ionic hydrosoluble functional groups, and an ionicco-monomer comprising ionic functional groups and hydrophobic functionalgroups, or a copolymer comprising four co-monomers, one providing thenon-ionic hydrosoluble functional groups, another providing hydrophobicfunctional groups, and two co-monomers providing ionic functional groupswith the same type of charge.
 29. The method of claim 26, comprisingcopolymerisation or co-condensation of a copolymer incorporating fourco-monomers, one providing non-ionic hydrosoluble functional groups, afurther providing ionic functional groups, and two co-monomers providinghydrophobic functional groups.
 30. A method of preparing the polymerfluid of claim 1, comprising adding non-ionic hydrosoluble functionalgroups, the ionic functional groups and the hydrophobic functionalgroups to an existing polymer by means of chemical reactions usingreactants capable of reacting with the polymer.
 31. The method of claim30, wherein the reactions include grafting or hydrolysis reactions. 32.A method of preparing the polymer fluid of claim 1, comprisingcopolymerization or co-condensation of at least two different monomers,one of which provides the non-ionic hydrosoluble functional groups and afurther monomer that provides the ionic functional groups and thehydrophobic functional groups and further comprising adding non-ionichydrosoluble functional groups, the ionic functional groups and thehydrophobic functional groups to an existing polymer by means ofchemical reactions using reactants capable of reacting with the polymer.33. A cosmetic formulation including the polymer fluid of claim
 1. 34. Afluid used to initiate the transmission of shear movement or wavesincluding the polymer fluid of claim
 1. 35. A method of treating wellsor underground reservoirs including the use of the polymer fluid ofclaim 1.